This invention relates to the field of micro electromechanical systems (MEMS), more particularly to methods used to coat the devices, more particularly to methods used to coat the devices with dissolved resins without structural damage.
Micro-electro-mechanical systems (MEMS) or micromechanical devices are micron-scale devices, often with moving parts, and are fabricated using traditional semiconductor processes such as optical lithography, doping, metal sputtering, oxide deposition, and plasma etching which have been developed for the fabrication of integrated circuits.
Micromirrors, such as the DMD(trademark) micromirror array from Texas Instruments, are a type of micromechanical device. Other types of micromechanical devices include accelerometers, pressure and flow sensors, gears and motors. While some micromechanical devices, such as pressure sensors, flow sensors, and micromirrors have found commercial success, other types have not yet been commercially viable.
MEMS devices are extremely robust on their own scale, but are easily destroyed by macroscopic forces such as capillary attraction. A MEMS device caught in the surface tension of a liquid will move with that liquid, bending or even breaking in the process. A droplet of water or organic solvent on a MEMS device will pull the device down as it evaporates. Even if the device is not irreversibly deformed, it is likely to be trapped in a bent state by surrounding devices.
The fragile nature of the MEMS devices can make them difficult to manufacture in a cost effective manner. In the case of micromirror arrays, once the sacrificial layers beneath the micromirror have been removed, the mirrors are very fragile and very susceptible to damage due to particles. The particles become trapped in the mechanical structure of the micromirror array and can prevent the micromirror from operating. Because the particles cannot be washed out of the array without destroying the array, it is necessary to separate the wafers on which the devices are formed, and wash the debris off the devices, prior to removing the sacrificial layers under the mirrorsxe2x80x94also called undercutting the mirrors. Furthermore, because the chip bond-out process also creates particles, it is desirable to mount the device in a package substrate and perform the chip bond-out process prior to undercutting the mirrors.
Unfortunately, it is only after the mirrors have been undercut that the micromirror array is able to be tested. Following a standard micromirror production flow, all of the devices manufactured are be mounted on package substrates, bonded-out to the substrates, and undercut prior to testing the devices. Additionally, micromirrors typically require some sort of lubrication to prevent the micromirror from sticking to the landing surfaces when it is deflected. Therefore, the devices must also be lubricated and the package lid or window applied prior to testing the devices. Because a typical micromirror package is very expensive, the packaging costs associated with devices that do not function greatly increase the cost of production and must be recovered by the devices that do function.
What is needed is a method of testing the micromechanical structure of a micromirror array prior to packaging the micromirror array. This method would enable a production flow that would only package the known good devices. Thus, the significant cost associated with the packaging the failed die would be eliminated.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention which provides a method and system for recoating MEMS devices using dissolved resins. One embodiment of the invention provides a method of coating free-standing micromechanical devices. The method comprising: depositing an organic resin coating material on a micromechanical device, the coating material comprised of at least 35% solids in a solvent, said coating material having a viscosity no greater than 120 centistokes; and curing the coating material.
Another embodiment of the invention provides a method of coating free-standing micromechanical devices. The method comprising: depositing an organic resin coating material on a micromechanical device, the coating material comprised of at least 35% solids in a solvent, the coating material having a viscosity no greater than 120 centistokes; rotating the micromechanical device to distribute the organic coating material; and curing the coating material.
Another embodiment of the invention provides a method of coating free-standing micromechanical devices. The method comprising: depositing an organic resin coating material on a micromechanical device, the coating material comprised of at least 35% solids in a solvent, the coating material having a viscosity no greater than 120 centistokes; and curing the coating material.
Another embodiment of the invention provides a method of coating free-standing micromechanical devices. The method comprising: depositing a solvent layer on a micromechanical device; depositing an organic resin coating material on solvent layer; allowing the organic resin coating material to displace the solvent layer; and curing the coating material.